The invention relates to an improved system for detecting underwater objects in a river or stream. More particularly, the system provides an improved means for doppler detection of underwater objects in a stream or river of varying velocity. In addition, the system rejects objects below a predetermined magnitued.
The use of doppler sonar systems in the past for the detection of swimmers, floaters or boats as targets has presented problems due to the plurality of speeds with which the target may advance in the water, the shifting velocity of the stream or river itself, and the fact that the detected object although moving in the stream may not be a desired target.